A Mirkwood spider. Warner Bros. gave this away a couple of months a go when there was a competetion. You had a series of multiple choice questions, one of which was something along the lines of : "which creature attacked Radagast at Rhosgobel?" Not being in the book, it confused a lot of people!

Some have speculated that this is fairly early on in AUJ - the spiders destroy his home, leading to Radagast fleeing. This may be the reason Radagast and Gandalf bump into each other near Trollshaws - perhaps Radagast is seeking Gandalf for aid?